Although most HIV vaccine approaches investigated in the past have focused on generating neutralizing antibodies against the virus, there is increasing evidence to suggest that the key to success of this endeavor lies in strategies for eliciting cellular antiviral immunity. The applicants have proposed experiments aimed at developing a peptide vaccine with the capacity to prime a cytotoxic T- lymphocyte (CTL) response in vivo aginst HIV-1 epitomes. The nef and gag proteins have been identified as the sites of potentially important epitomes and will be the primary focus of their work. In order to prime a CTL response, a CTL epitome-containing protein must be delivered to the cytosol of mammalian cells. There, it is processed to form peptides which are then complexed with MH class I molecules and presented at the cell surface. Recent studies have revealed how the intra cellularly acting toxin, such as the anthrax toxin (AT), may be modified to ablate its toxicity and enable it to deliver heterologous proteins to the mammalian cell cytosol. As a ramification of these findings, the applicants have demonstrated that AT fusion proteins containing selected epitomes from Listeria monocytogenes and lymphocytic choriomenigitis virus may be used to prime protective CTL responses in mice against these pathogens. In the research proposed, the applicants intend to prepare similar AT fusions continuing the nef and gag proteins and test these constructs for ability to prime an antigen-specific CTL response in mice. Furthermore, the applicants will also attempt to determine whether human cells treated invitro with these fusions can induce proliferation of gag- and nef-specific CTL from peripheral blood ofpatients infected with HIV. Finally, the researchers will investigate whether patient-derived gag- and nef-specific CTL can lyse haplotype-matched target cells treated with the fusion proteins. These experiments will allow the utility of the AT-based vaccine strategy to generate a CTL response against HIV antigens to be evaluated and, if positive indications are obtained, will set the stage for safety and efficacy studies of AT-based vaccines in primate animal models.